1. Field of the Invention
This invention relates to a polypropylene resin composition. More specifically, it relates to a polypropylene composition suitable for a large molding such as an automobile bumper.
2. Description of the Related Art
A polypropylene resin has often been used when molding such products as automobile bumpers because it is light, corrosion-proof, and intricately shaped products such as automobile bumpers can be easily molded from said resin.
Although a polypropylene resin is thought to be suitable for an automobile bumper, an automobile bumper made of a polypropylene resin does not have enough impact strength, and does not paint well. Recently, a polypropylene resin composition composed of a polypropylene polymer, an ethylene-propylene rubber, and an inorganic filler was used for an automobile bumper to improve the impact strength and paintability of the bumper. Japanese Unexamined Patent Publication (Kokai) No. 55-21494 discloses a composition of polyolefin such as an isotactic polypropylene, high density polyethylene, low density polyethylene, or ethylene-propylene copolymer, an elastomer such as ethylene-propylene rubber or ethylene-propylene-diene terpolymer, and an inorganic filler. Japanese Kokai Nos. 57-55952 and 58-111846 disclose a composition of a crystalline ethylene-propylene block copolymer, an amorphous ethylene-propylene copolymer, and a talc. Japanese Kokai No. 57-159841 discloses a composition of a crystalline ethylene-propylene block copolymer, an amorphous ethylene-propylene copolymer, a high density polyethylene, and a talc. Japanese Kokai No. 57-195134 discloses a composition of a polypropylene polymer, an elastomer, a compound selected from aromatic sulfonic acid, an aromatic carboxylic acid, a C.sub.4 to C.sub.12 aliphatic dicarboxylic acid, an aromatic phosphine, a metallic salt of the aromatic phosphine, and a dibenzylidene sorbitol, and an inorganic filler. Japanese Kokai Nos. 57-207630 and 58-17139 disclose a composition of a crystalline polyolefin, an ethylene-.alpha.-olefin rubber, and an inorganic filler selected from talc, mica, and calcium silicate.
An automobile bumper molded from these compositions, although improved in impact strength, has a poor appearance, poor surface hardness, and poor paintability (i.e. paint coated on the automobile bumper is easily scratched off).